1. Field of the Invention
This invention relates generally to train control systems, and more specifically to a train control system that combines certain structures of cab-signaling technology with structures used in communication based train control (CBTC) technology. A hybrid train control system employs traditional wayside fixed blocks with associated cab-signal control devices, as well as intelligent CBTC carborne equipment. The cab-signal control devices generate discrete speed commands that are injected into the running rails of the various cab-signaling blocks. In turn, an intelligent CBTC carborne device determines the location of the associated train, and generates a movement authority limit (MAL) based on the speed commands received from the wayside cab-signaling devices.
2. Description of Prior Art
Cab-signaling technology is well known, and has evolved from fixed block, wayside signaling. Typically, a cab-signal system includes wayside elements that generate discrete speed commands based on a number of factors that include train detection data, civil speed limits, train characteristics, and track geometry data. The speed commands are injected into the running rails of the various cab-signaling blocks, and are received by trains operating on these blocks via pickup coils. A cab-signal system also includes carborne devices that present the speed information to train operators, and which ensure that the actual speed of a train does not exceed the speed received from the wayside.
CBTC technology is also known in the art, and has been gaining popularity as the technology of choice for new transit properties. A CBTC system is based on continuous two-way communications between intelligent trains and Zone controllers on the wayside. An intelligent train determines its own location, and generates and enforces a safe speed profile. There are a number of structures known in the art for a train to determine its own location independent of track circuits. One such structure uses a plurality of passive transponders that are located on the track between the rails to provide reference locations to approaching trains. Using a speed measurement system, such as a tachometer, the vital onboard computer continuously calculates the location and speed of the train between transponders.
The operation of CBTC is based on the moving block principle, which requires trains in an area to continuously report their locations to a Zone Controller. In turn, the Zone Controller transmits to all trains in the area a data map that contains the topography of the tracks (i.e., grades, curves, super-elevation, etc.), the civil speed limits, and the locations of wayside signal equipment. The Zone controller, also, tracks all trains in its area, calculates and transmits to each train a movement authority limit. A movement authority is normally limited by a train ahead, a wayside signal displaying a stop indication, a failed track circuit, an end of track, or the like. Upon receiving a movement authority limit, the onboard computer generates a speed profile (speed vs. distance curve) that takes into account the limit of the movement authority, the civil speed limits, the topography of the track, and the braking characteristics of the train. The onboard computer, also, ensures that the actual speed of the train does not exceed the safe speed limit.
CBTC has a number of advantages over cab-signaling technology, including shorter headways, enforcement of temporary speed limits, and enabling trains with different traction and braking characteristics to operate on the same line.
While the benefits and advantages of CBTC are well known, it is difficult to migrate a cab-signaling installation to a CBTC installation. Also, when implementing an extension to an existing line controlled by cab-signaling, a transit or a rail property is normally limited to a single choice, namely to use the same train control technology that is used on the existing line. In addition, it is desirable to standardize the man-machine-interface provided by cab-signaling and CBTC systems. Further, it desirable to achieve a certain level of interoperability between cab-signaling and CBTC. The current invention provides a structure that facilitates the migration from cab-signaling to CBTC, enables the use of CBTC technology on an extension of a line that is controlled by cab-signaling, provides a man-machine-interface for cab-signaling systems that is based on the distance-to-go format, and enables CBTC equipped trains to operate with wayside cab-signaling devices.